Resin harvest. Resin (white) running from a cut in the trunk of a pine tree (Pinus sp.) into a collecting cup. Resin is an acidic polymer that is secreted by many trees in response to injury. It can be harvested many times from the same tree over a period of several years. Traditionally, resin was collected and used for making rosin, a substance used for waxing the bows of stringed instruments, as well as turpentine. However, cheaper synthetic alternatives are now available, meaning that resin harvesting has become less common. Photographed in Santo Andre, Portugal.